The present invention relates to a disk array apparatus and, more particularly, to a disk array apparatus for automatically assigning a defective alternate block within the apparatus when an uncorrectable medium fault is detected.
A known example of the technique for increasing the reliability of magnetic disk devices is a disk array apparatus for storing and reading out data or redundant data such as calculated parity data in and from a plurality of magnetic disk devices. In the computer field, the magnetic disk device for storing data is being demanded for higher reliability, larger capacity, higher performance along with higher performance of the CPU (Central Processing Unit) and a larger data amount processed by the computer system. The disk array technique receives a great deal of attention as a magnetic disk application technique which meets these demands.
Even if a disk fails, the disk array apparatus can reconstruct data stored in the faulty magnetic disk using redundant data such as parity data to normally input/output data from/to a host computer. A technique using this feature of the disk array apparatus has already been proposed. According to this technique, when processing is done upon reception of a read instruction from the host computer, a disk delayed in response owing to an uncorrectable medium fault retry within the magnetic disk device is temporarily disconnected. Readout data is generated using remaining magnetic disk device data and sent to the host computer to guarantee the response performance to the host computer.
Japanese Patent Laid-Open No. 7-200191 discloses the technique of temporarily disconnecting a disk delayed in response, and when the disk device reports an uncorrectable medium fault, setting a defective alternate block within an apparatus.
The conventional disk array apparatus assigns a defective alternate block immediately when an uncorrectable medium fault occurs in the disk device.
The causes of the uncorrectable medium fault in the disk device are a scratch or damage on the magnetic disk medium surface, dust or foreign substance attached to the medium surface or write/read head, degradation in read characteristics of the write/read head due to a temperature change, and the like. If a scratch or damage on the magnetic disk medium surface causes an uncorrectable medium fault, a defective alternate area can be quickly assigned to the block having the medium fault.
If dust on the medium surface or the temperature of the write/read head causes an uncorrectable medium fault, this fault is temporary and may be canceled to normally read data upon removal of dust from the medium surface or a temperature change in write/read head. In this case, although the fault is not an actual medium fault, defective alternate processing is executed to consume an alternate block.
It is an object of the present invention to provide a disk array apparatus capable of reducing consumption of defective alternate blocks of a magnetic disk when the defective alternate block of the magnetic disk medium is assigned in the disk array apparatus upon occurrence of an uncorrectable medium fault.
To achieve the above object, according to the present invention, there is provided a disk array apparatus comprising detection means for detecting a faulty magnetic disk device delayed in response to a read instruction from a host device out of a plurality of magnetic disk devices constituting an array, delay means for outputting a delay signal on the basis of an output from the detection means, instruction issue means for issuing a retry instruction to the faulty magnetic disk device on the basis of the delay signal from the delay means, first determination means for determining in response to the retry instruction from the instruction issue means whether the faulty magnetic disk device normally ends read processing, and assignment means for assigning a defective alternate block to the faulty magnetic disk device when a determination result of the first determination means does not represent a normal processing end.